Overloaded breaker or Short circuit?

[tommya.meyers]

I went over to help a buddy with a 15 amp circuit he had trip over the weekend. It’s on a 15 amp single pole tandem breaker. The circuits has loads such as his TV, computer, and about 4-6 can lights(so basically around 5 receps and 6 can lights controlled by 2 dimmer switches) . The breaker was in the tripped position when I got there, so I cycled it off then I tried to switch it back on and working a second it hummed then tripped. Tried it a few more times with the same results. I removed the circuit and applied it to the second 15amp breaker of the tandem and the same thing happened, a hum noise then a trip all within 2 seconds max. I put another working 15 amp circuit on it to make sure the breaker wasn’t bad and sure enough it energized and held and was reading 120v to ground on the load side. I also moved the circuit to another single pole 15 amp breaker that wasn’t a tandem to make sure it wasn’t just the whole breaker itself and sure enough it tripped that breaker as well so it’s either a short or an overlord. He said he hasn’t added anything at all to the circuit to make it overload. I asked if he’s driven any screws or nails into the walls as well Incase he may have hit the Romex and that was ruled out. So I unplugged all of the loads, even removed a few of the receptacles and just wired the wires together to see if I could get the circuit breaker to hold, but no luck. I checked for continuity at the recaps and I was reading it but that could be because it’s getting the continuity from the can lights. So I pretty much ruled out an overload of the circuit, and now onto finding a short. We only had 30 minutes to mess around with it today but I will be going back tom. My plan is to find the home run of the circuit coming into the nearest receptacle to the panel id imagine and identify it and take any load off it and see if the breaker energizes and holds and reads 120v to ground. If I get that far then I will start attaching load by load down the stream until I find out which load is tripping the circuit. Any advice would help and be greatly appreciated. Should I remove the bulbs in the can lights to remove more power draw or that being the possibility of the short?

[trader_4]

On Monday, April 20, 2020 at 11:49:29 PM UTC-4, [e-mail] wrote:

With the light switch off, the lights should not be a factor. With a tandem breaker, it must be a shared neutral circuit, so be aware of that. Any chance there is another receptacle/load on the circuit that's not obvious? Sounds like you are on the right track. I would take a look at all the boxes first, pull the receptacles, switches out, see if anything is obvious.

[Dean Hoffman]

On 4/20/20 10:49 PM, [e-mail] wrote:

Can you go halfway down the circuit distance wise and unhook everything down stream? Does the breaker trip then?

[Wade Garrett]

On 4/20/20 11:49 PM, [e-mail] wrote:

See that big key on the right hand side of your keyboard marked "Return" of "Enter"?

Try hitting it once in a while to make paragraphs so people can read your post ;-)

[TimR]

Something went bad on a circuit that used to work.

Could be any of the appliances on receptacles. But you unplugged them.

Could be a short in a receptacle. I've seen it, but rarely. In my limited experience these tend not to behave like an overload, but like a short. Your symptoms sound like overload rather than short. Same for wiring.

Can't be a short in a bulb. Those usually just blow.

So, what's left? The dimmer. That is the first place I'd look. I've seen a lot of these go bad.

Why start at the breaker? I usually start at the other end.

[Ralph Mowery]

The first thing to do is unplug if possiable and turn off everything on the circuit. Then instead of just flipping the breaker back on more than once, use an ohm meter to check the circuit for a short. If none found, turn the breaker back on and test each device before you turn it on or plug it in. just do one at a time. sooner or later you will find the defective device. It does help to have an amp meter to actually see how much current is being used as the devices are turned back on.

If breakers are continiously turned on and tripped it won't be long before the breaker will fail or be weakened.

Lowes has some test meters for around $ 50 and I am sure other stores have the same or similar.

[TimR]

I had to look this up sometime back and I've probably posted the exact numbers.

But it turns out a breaker can trip on a mild overload quite a lot of times, many thousands.

A direct short is another matter. On average you get only 2 tries before failure, and it might be the 1st time.

The last time we had this discussion it was a handyman electrician recommending his method for figuring out what breaker an outlet was on. He put together a plug with the prongs hard wired together. Then he would plug it in and go look for the breaker that had tripped. I was then and remain horrified at that idea. Clearly it would work, but you're stressing every part of that circuit.

[Clare Snyder]

Don't bet the farm on it. I've had nimerous 12 volt automotive bulbs short, and a few 120 volt incandescents. Had one Compact flourescent that would pop fuses.

And I've NEVER seen one short to ground. Generally the blow open, and if they fail closed they just keep the lights on.

Generally start in the middle of the circuit, then in the middle of the sector that fails. Most likely cause is a black wire shorted to grounf - like a wire nut fell off - or a wire pinched. Is it Romex or sheilded cable or conduit???

[TimR]

Now I'll predict the worst case.

He'll go back tomorrow filled with our suggestions - and nothing he can do will get the breaker to trip again.

I hate it when that happens.

[Ralph Mowery]

I would agree start in the middle and work by halfs , but in many houses it is hard to know where the middle is.

[trader_4]

Did you ever see it with the light switch off?

[Clare Snyder]

Not if you know what all is on the circuit and think like an electrician. Throw a fox and hound into the equation and it becomes pretty trivial to figure it out (an active signal tracer)

[Sam E]

[snip]

How about a device that creates a 100% overload (like 40A on a 20A breaker), which is a lot less than infinite? Still don't leave it connected more than a second or so.

[TimR]

How would you do that? Buy a big toaster? Daisy chain a half dozen hair dryers?

I thought of hardwiring a 30A breaker and plugging that in, but there's no guarantee it wouldn't trip first.

At any rate, the original poster has ghosted us, we'll never know what is wrong, so we can all confidently claim to have been right.

[Mark]

He should also ask his friend if he has put any nails / screws in the walls etc to hang pictures :)

[dpb]

...

????

[Clare Snyder]

A decent breaker should protect against a short circuit numerous times. The short circuit trip is MAGNETIC.

On the other hand, a breaker that has tripped due to repeated overloads will deteriorate because the overload trip is thermal. Even running "on the edge" repeatedly will cause a breaker to eventually fail (usually causing it to trip prematurely unless it's a FPC/FPE breaker)

[Mark]

Nothing like a nail driven through a wire to cause a short

[TimR]

I've seen it argued both ways. Very possible over the years I've argued it both ways. I found this snip in a similar thread some years back:

**** One Square D breaker I found data for was rated at 12,500 cycles mechanical operation (meaning you turned it off by hand) and 2,800 electrical operation (meaning it overloaded but did NOT fault). I would think mechanical operation would depend on how much current was being drawn at the time, and I always try to turn off loads before flipping a breaker just in case. We had a nasty explosion in the plant once when somebody flipped a disconnect under load.

I could not find the fault rating for that breaker but several other searches said a breaker is guaranteed to interrupt the full fault current (meaning a short) ONCE, and should be replaced after twice.

*****

[dpb]

Not on just a small household circuit type load nor a household-sized breaker, either, I'll bet.

I'm having a hard time believing a manufacturer would say that on a household-sized breaker, sorry.

I've never seen one replaced because of a short-circuit trip and never heard one failing in such a fashion after.